Method of machining tapered roller bearing inner rings

ABSTRACT

A method of machining tapered roller bearing inner rings, wherein after the inner ring raceway groove 14 has been finish-ground, the inner ring small end face 13 and cone back face rib surface 12 are simultaneously finish-ground. In the manufacture of double row tapered roller bearings, in order to ensure that the assembly clearance which is produced during assembly of double row tapered roller bearings is always maintained constant, the method is intended to finish the raceway groove diameter to a predetermined dimension on the basis of the small end face 13, even if there is a variation in the diameter of the raceway groove 14 of each tapered roller bearing. Thus, the method comprises converting any deviation of the raceway groove diameter from a target dimension into a deviation in the inner ring axial direction, feeding the converted value back to an in-process control gauge 30 for controlling grinding operation, and simultaneously grinding the small end face 13 and cone back face rib surface 12 of the inner ring 10 by an end face grinding stone 42 and a rib grinding stone 41 integrally connected with the former, under the control of the gauge.

This invention relates to a method of machining the inner rings oftapered roller bearings. More particularly, it relates to a method ofmachining the inner rings of double row tapered roller bearings ortapered roller bearings used in a double row, such as back-to-backduplex tapered roller bearings, and particularly to a method ofmachining tapered roller bearing inner rings in such a manner as toensure that the dimension from the outer ring back face (small end face)to the inner ring front face (small end face), i.e., the planedifference, and the bearing assembly clearance (axial clearance) due tothat plane difference are constant.

This assembly clearance refers to such a dimension that when two innerring assemblies (comprising an inner ring, a retainer, and rollers) arecombined for manufacture (assembly), e.g., of a double row taperedroller bearing and the front faces of the inner rings are butted againsteach other by a predetermined force, the outer ring is allowed to moveaxially under a predetermined measuring load. The assembly clearance,when bearings are assembled into a machine (e.g., on automobile axles),determines the running clearance and hence it is closely related toseizure, premature peeling, etc., greatly influencing the bearing life;thus it is one of the important conditions for bearing assembly.

Generally, the assembly clearance (axial clearance) of this type ofbearing is determined by the plane difference of the bearing assembly.Of the dimensions of the various surfaces of the inner ring, those whichinfluence the plane difference are the raceway groove diameter of theinner ring (the smaller the diameter, the smaller the plane difference;in other words, as viewed from the outer ring back face, the inner ringfront face is positioned further onwards), the cone back face rib widthor, briefly, rib dimension (the smaller the dimension, the smaller theplane difference), and the width (the smaller the width, the greater theplane difference: in other words, as viewed from the outer ring backface, the inner ring front face is positioned further backwards).

Conventionally, this type of bearing inner ring is machined in the orderof width surfaces--raceway groove--cone back face rib surface. However,since each is machined according to its independent target point, thefinal finish dimension in each surface has an independent variation. Asa result, despite the fact that each surface has been finished withinthe limits of its predetermined tolerance, it has been impossible tokeep the bearing assembly clearance (axial clearance) under strictcontrol.

This will now be described in more detail with reference to the finishdimension of the rolling groove.

If the plane difference from the outer ring back face to the inner ringfront face with the raceway groove machined to a finish dimension basedon the inner ring front face (in the case of a double row tapered rollerbearing, the dimension from the outer ring width center to the frontface of each inner ring) can be maintained constant, the tolerance canbe strictly controlled and assembly can be performed without using aspacer for filling the axial clearance of the bearing assembly. However,the conventional method has been by attractively holding thefinish-ground inner ring back face (large end face) of the bearing innerring on the backing plate of a grinding machine, and grinding theraceway groove by a grinding stone by rotating the backing plate andinner ring while measuring the raceway groove diameter by an in-processcontrol gauge (which controls grinding operation) positioned apredetermined distance away from the backing plate. Since this is basedon the measurement of the raceway groove diameter at that fixed positionspaced away from the inner ring back face, it follows that the racewaygroove is machined on the basis of the inner ring back face. When viewedfrom the inner ring front face providing a basis for the planedifference dimension, the position at which the rolling groove ismeasured differs for each workpiece and so does the measured dimensionbecause of a variation (which is within the limits of the predeterminedtolerance) in the width of the inner ring.

Consequently, the conventional practice has, in assembly operation, beento place a spacer of predetermined thickness between the opposed frontfaces of two inner rings so as to absorb the dimensional error toprovide a predetermined axial clearance (FIG. 1). Further, where twotapered roller bearings are assembled in back-to-back relation, likewisea spacer of predetermined thickness is interposed. Such practice,therefore, is required to prepare a number of spacers of differentthicknesses in advance and a suitable spacer must be selected for eachassembly of a bearing in accordance with the actual inner ring width,thus greatly detracting from operation capability (bearing assemblingefficiency) and interchangeability (for example, a mating inner ring islimited).

The present invention is intended to eliminate the conventional problemsdescribed above and provide a method of machining the inner rings oftapered roller bearings in such a manner that the plane difference andthe bearing assembly clearance depending thereon are maintainedconstant.

To this end, the method of this invention comprises the steps ofgrinding the raceway groove on the basis of the back face of an innerring whose opposite end faces, i.e., the front face and back face havebeen ground by the usual grinding method in the preprocessing step, andsimultaneously grinding the front face and cone back face rib surface byan end face grinding stone and a rib grinding stone which are connectedtogether. According to the method of the invention, the finish-groundinner ring raceway groove is measured in advance; the deviation of theraceway groove finish dimension from a target dimension is convertedinto a deviation in the inner ring axial direction; the converted valueis fed back to an in-process control gauge; and controlling the grindingoperation is controlled by this gauge. Therefore, in this invention,even if there is a variation in the finish width in the preprocessingstep and even if this variation results in a variation in the racewaygroove diameter, the rolling groove diameter can be finished based onthe front face to a predetermined value without being-influenced by suchvariations, ensuring that the axial clearance produced when the innerring is combined with the outer ring is constant. Thus, in the case ofassembly of double row tapered roller bearings or of bearings inback-to-back double row relation, such assembly can be performed withoutthe need of adjusting the axial clearance and with no spacer or a singlekind of spacers used, thus improving operation capability for assemblingbearings and making it possible to strictly set the axial clearance(preload) when this bearing is incorporated in a machine (e.g., on anautomobile axle). Further, in the present invention, since the finishwidth is feedback-controlled on the basis of the raceway groove diameterhaving less variation in the finish width, the amount of feedback can beminimized and control can be performed easily yet accurately. Further,in the present invention, since the dimension from the front face to thecone back face rib surface can be always maintained constant ingrinding, the dimension from the front face to the cone back face ribsurface can be simultaneously finished to the predetermined dimension(value with the variation in the rolling groove diameter taken intoconsideration) by simply feeding the axial length value corresponding tothe deviation of the measured raceway groove diameter from the referencevalue back to an in-process control gauge contacted with either the coneback face rib surface or the front face.

Further, in this invention, when the inner ring front face and cone backface rib surface of a bearing inner ring having undergone raceway groovegrinding on the basis of the inner ring back face are simultaneouslyground by the end face grinding stone and the rib grinding stoneconnected together, the raceway groove diameter is measured in advanceand if the cone back face rib dimension measured before machining by thein-process control gauge is outside the range of upper and lower limitsof preset machining allowance with respect to the machining allowancefor the cone back face rib surface necessary to ensure that the planedifference calculated on the basis of the measured value of the racewaygroove diameter taken in advance has a predetermined dimension, thecorresponding bearing inner ring is off-lined as an NG article beforemachining. Therefore, in this invention, if the cone back face ribsurface machining allowance is inside the predetermined range, the frontface and cone back face rib surface are simultaneously ground by the endface grinding stone and rib grinding stone connected together, and ifthe cone back face rib surface machining allowance is outside the rangeof predetermined upper and lower limits of machining allowance, thecorresponding bearing inner ring is off-lined as an NG article, therebypreventing the skin of the inner ring cone back face rib surface frombeing left uncut or abnormal scaling-off from taking place in the ribgrinding stone.

These and other objects and features of this invention will become moreapparent from the following description to be given with reference tothe accompanying drawings, in which:

FIG. 1 is a sectional view of a conventional double row tapered rollerbearing using a spacer;

FIG. 2 is a schematic view for an explanation of a machining methodaccording to an embodiment of this invention;

FIG. 3 is a sectional view of a double row tapered roller bearingassembled with no spacer and including an inner ring machined by themachining method of this invention;

FIG. 4 is a schematic view for an explanation of another embodiment of amachining method according to this invention;

FIG. 5 is a flowchart of the procedure involved in the same embodiment;and

FIG. 6 is a schematic view showing the machining principle of thisinvention.

Embodiments of the invention will now be described with reference to thedrawing. In addition, throughout the figures like reference numeralsindicate like parts or portions.

In FIG. 2, the numeral 10 denotes a tapered roller bearing inner ringattractively held on the backing plate 20 of a grinding machine; 21denotes a rib grinding stone for grinding the rib surface 12 of the coneback face rib 11 of the inner ring 10; 22 denotes an end face grindingstone for grinding the front face, i.e., small end face 13 of the innerring 10; 23 denotes a rotary dresser for the rib grinding stone; and 24denotes a rotary dresser for the end face grinding stone. The ribgrinding stone 21 and end face grinding stone 22 are concentricallyarranged on a grinding stone spindle 25 through a grinding stone spacer26 and in constant diameter dimensional relation and fixed by a flangenut 27 and adapted to grind the cone back face rib surface 12 and frontface 13 of the inner ring 10 by their outer peripheral surfaces 21a and22a. The numeral 28 denotes a grinding stone flange. The rotary dresser23 for the rib grinding stone has the angle of its front end face 23aadjusted and is fixed to a dress compensation slide (not shown), whilethe rotary dresser 24 for the end face grinding stone is arranged sothat its front end face 24a is revolvable in a horizontal plane withrespect to the rotary dresser 23 for the rib grinding stone, the dresser24 having a dress compensation slide (not shown). The numeral 30 denotesa first measuring instrument for in-process control attached to thefixed block (not shown) of the grinding machine and adapted to bebrought into contact with the front face 13 of the inner ring 10 formeasuring the width dimension from the end face of the backing plate 20to the front face 13 of the inner ring 10; and 31 denotes a secondmeasuring instrument for measuring the raceway groove diameter of theinner ring 10 at a position spaced a fixed distance from the end face ofthe backing plate 20.

The machining method of this invention in the above arrangement will nowbe described. The back face of the bearing inner ring 10 whose racewaygroove 14 has been ground to a target dimension based on the back face,i.e., large end face without regard to the width of the workpiece by theusual grinding method in the preprocessing step is attractively held onthe backing plate 20, and the first measuring instrument 30 is buttedagainst the front face 13 of the inner ring 10 and the second measuringinstrument 31 is butted against the raceway groove 14, so as to measurethe width and raceway groove diameter of the inner ring 10. At thistime, the deviation (machining error) of the raceway groove diametermeasured by the second measuring instrument 31 from a reference racewaygroove diameter (target dimension in engineering design) is calculatedand this deviation value is converted into a deviation value in theinner ring axial direction, the converted value being fed back to thefirst measuring instrument. Subsequently, the cone back face rib surface12 and front face 13 of the inner ring 10 are simultaneously ground bythe rib grinding stone 23 and end face grinding stone 24 connectedtogether in constant diameter dimensional relation, until the measuredvalue provided by the zero-point calibrated first measuring instrumentis equal to the predetermined inner ring width.

This manner of grinding results in the raceway groove diameter of theinner ring 10 being set in accordance with the inner ring width, so thatthe raceway groove diameter is maintained constant based on the frontface 13 for each inner ring, enabling back-to-back bearing assembly tobe made without any spacer, as shown in FIG. 3, or using a single kindof spacers, thus improving operation capability.

FIG. 4 is a schematic view showing how the cone back face rib surfaceand front face of a bearing inner ring are simultaneously ground by amethod according to another embodiment of the invention.

In the same figure, 41 denotes a rib grinding stone for grinding thecone back face rib surface 12 of the inner ring 10; 42 denotes an endface grinding stone for grinding the front face 13 of the inner ring 10;43 denotes a rotary dresser for the rib grinding stone; and 44 denotes arotary dresser for the end face grinding stone. The rib grinding stone41 and end face grinding stone 42 are coaxially arranged on a grindingstone spindle in constant diameter difference dimensional relation andthrough a grinding stone spacer 46 and fixed by a flange nut 47 andadapted to grind the cone back face rib surface 12 and front face 13 ofthe inner ring 10 by their outer peripheral surfaces 41a and 42a. Thenumeral 48 denotes a grinding stone flange. In addition, the rotarydresser 43 for the rib grinding stone and the rotary dresser 44 for theend face grinding stone are coaxially fixed on a dress spindle 49through a spacer 50. The dress spindle 49 is fixed to a dresscompensation slide (not shown) while forming an angle with the grindingstone spindle 45, and a positional adjustment is made so that the anglebetween the front end face 44a of the rotary dresser 44 for the end facegrinding stone and the front end face 43a of the rotary dresser 43 forthe rib grinding stone is equal to the angle between the cone back facerib surface 12 and front face 13 of the bearing inner ring 10. Indicatedat 30' is a first measuring instrument for in-process control attachedto the grinding machine and adapted to be brought into contact with thecone back face rib surface 12 of the inner ring 10 for measuring the ribdimension (axial width of the cone back face rib) from the end face ofthe backing plate 20 to the cone back face rib surface 12 of the innerring 10. The second measuring instrument 31 is attached to the grindingmachine as in the embodiment shown in FIG. 2, for measuring the diameterof the ground raceway groove of the inner ring 10.

The machining method, in the above arrangement, will now be describedwith reference to the flowchart shown in FIG. 5. The back face of thebearing inner ring 10 whose opposite end faces have been ground by theusual grinding method in the preprocessing step and whose raceway groovehas been ground to a target dimension based on the back face isattractively held on the backing plate 20, and the first and secondmeasuring instruments 30' and 31 are butted against the cone back facerib surface 12 and raceway groove 14 of the inner ring 10, respectively,for measuring the rib dimension and raceway groove diameter of the innerring 10. At this time, the deviation (machining error) of the racewaygroove diameter measured by the second measuring instrument 31 from thereference raceway groove diameter (target dimension in engineeringdesign for securing a predetermined plane difference) is calculated, andthis deviation value is converted into a deviation value in the innerring axial direction (a deviation value converted into a planedifference dimension), the converted value being fed back to the firstmeasuring instrument 30'. It is then calculated how much the cone backface rib surface 12 should be ground to secure the predetermined planedifference with the zero-point calibrated first measuring instrument30', so as to find the machining allowance for the cone back face ribsurface 12 of the inner ring 10. Of course, the grinding operation iscontrolled by the first measuring instrument 30'.

Whether or not this machining allowance S is larger than the lower limitN of preset machining allowance S is judged, and if it is found to besmaller than the lower limit N, the corresponding inner ring 10 isoff-lined as an NG article. If it is found to be larger than the lowerlimit N, it is then judged whether or not the machining allowance S issmaller than the upper limit of preset machining allowance S, and if itis found to be larger than the upper limit M of machining allowance S,it is judged to be an excessive machining allowance and again thecorresponding inner ring 10 is off-lined as NG article. If the machiningallowance S is found to be within the predetermined range, the cone backface rib surface 12 and front face 13 of the inner ring 10 aresimultaneously ground by the rib grinding stone 41 and end face grindingstone 42 connected together in constant diameter difference dimensionalrelation, until the machining allowance S is zero, while performingin-process control by the zero-point calibrated first measuringinstrument 30' as in the embodiment shown in FIG. 2.

Grinding the cone back face rib surface 12 and front face 13 of theinner ring 10 in this manner results in the raceway groove diameter ofthe inner ring 10 being set in accordance with the inner ring width, sothat the raceway groove diameter based on the inner ring front face 13is maintained constant and hence the plane difference or axial clearanceof the bearing assembly is maintained constant. Thus, in the case ofback-to-back assembly, this can be performed with no spacer, as shown inFIG. 3, or a single kind of spacers used, thus improving operationcapability.

Further, it is possible to prevent skin removing (unground surface) fromtaking place in the cone back face rib surface 12 or abnormalscaling-off from taking place in the rib grinding stone owing toexcessive cut. Further, since the rib grinding stone rotary dresser andthe end face grinding stone rotary dresser for dressing the rib grindingstone and end face grinding stone are coaxially supported on a singledress spindle, it is possible to prevent the distance between the ribgrinding stone and the end face grinding stone from varying with thevariation of conditions during dressing.

Stated in more detail, the machining method of the present invention, asshown in FIG. 6, simultaneously grinds the cone back face rib surface 12and front face 13 of the inner ring 10, whose raceway groove has beenfinish-machined in the preprocessing step, using the in-process controlgauge 30, 30' zero-point calibrated in accordance with the finishedraceway groove diameter. Since the rib grinding stone 21, 41 and the endface grinding stone 22, 42 are connected together in constant diameterdimensional relation (the separation distance being constant), thedistance K between the cone back face rib surface 12 and front face 13of the ground inner ring 10 is always maintained constant. Thus,assuming that the raceway groove diameter at distance P from the backface of the inner ring 10 has been finished ΔR in terms of radiusgreater than the reference raceway groove diameter R. In order to makethe raceway groove diameter at position Q from the inner ring front faceequal to the reference raceway groove diameter R, the grinding of theinner ring front face must be terminated ΔD short.

This ΔD is expressed by the following equation: (ΔD/ΔR)= cot β∴ΔD=ΔR cotβ. Therefore, in the case of the embodiment shown in FIG. 4, if thezero-point for the cone back face rib dimension measured by the firstmeasuring instrument 30' is fed back ΔD short and the cone back face ribsurface 12 is ground until the cone back face rib dimension is Yo, thenit follows that the distance from the cone back face rib surface 12 tothe inner ring front face 13 is finished to the reference dimension Kand that at the same time the raceway groove diameter at the position ofdistance Q from the inner ring front face 13 is R. Therefore, there isno possibility of the dimensions of the portions 12, 13 and 14 of theinner ring being influenced by the width dimension including machiningerrors, and the plane difference for each inner ring can be madeconstant. As described, according to the method of the invention, if theraceway groove diameter at the position of distance P from the back facehas been finished ΔR in terms of radius greater than the referencedimension R in engineering design, this inner ring 10 will be finishedwith a width Xo and a cone back face rib dimension Yo. In addition, Xand Y represent base values in engineering design for the width and therib dimension, respectively.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

What is claimed is:
 1. A method of machining tapered roller bearinginner rings comprising the steps of:grinding a raceway groove of saidinner ring; measuring a raceway groove diameter at a fixed axialdistance away from a cone back face of said inner ring; converting anydeviation of said raceway groove diameter from a target dimension into adeviation in the inner ring axial direction; feeding back said convertedvalue to an in-process control gauge for controlling subsequent grindingof a front face and cone back face rib surface of said inner ring; andsimultaneously grinding the front face and cone back face rib surface ofthe inner ring, respectively, by an end face grinding stone and a coneback face rib grinding stone which are connected together, the amount ofstock removal by said grinding stones being determined by ceasinggrinding in response to a stop signal supplied by said in-processcontrol gauge when said target dimension is achieved.
 2. A method as setforth in claim 1, wherein said in-process control gauge is applied tothe front face of the inner ring to measure the width of the inner ring.3. A method as set forth in claim 1, wherein said in-process controlgauge is applied to the cone back face rib surface of the inner ring tomeasure the cone back face rib width.
 4. A method as set forth in claim3, wherein whether or not the machining allowance for the cone back facerib surface is within a preset range is judged by said in-processcontrol gauge before the grinding of the cone back face rib surface, andif it is found to be within said range, the front face and cone backface rib surface of the inner ring are simultaneously ground,respectively, by the end face grinding stone and rib grinding stoneconnected together.